Compressor blade structure



Dec. 3, 1963 P. FoRTEscUE 3,112,866

COMPRESSOR BLADE STRUCTURE Filed July 5, 1961 2 Sheets-Sheefl l Dec. 3, 1963 p FORTESCUE 3,112,866

COMPRESSOR BLADE STRUCTURE l Filed July 5, 1961 2 Sheets-Sheet 2 fao :a6 l fg- 4 l/ Pfsw/,QL [6 Pfff/P Paw-5 caf United States Patent O 3,112,366 CMPRESSUR BLADE STRUCTURE Peter Fortescue, Rancho Santa Fe, Qalif., assigner to General Dynamics Corporation, New York, NSY., a corporation of Delaware Filed .luly 5, lQdEl, Ser. No. l2i,375 4 Claims. (6l. Z39-M2) This invention relates to compressor blading and more particularly lto an improved compressor blade structure of the type suitable for use in an axial flow compressor.

The conventional axial flow type of gas compressor has proven to work most effectively with an internal gas elocity close to but somewhat belowlocal sonic velocity. This stems from the fact that the static pressure ratios obtainable within a gas compressor are related to the lach numbers induced, and the ratios substantially increase as the Mach number is raised. However, a limit is set on the amount of compression obtainable by the fact that control of the high velocity gas flow becomes extremely more difficult as the flow reaches supersonic velocities, and blade losses are correspondingly high under these circumstances. In normal practice, therefore, compressors are designed to work with gases having relative velocities just below local sonic velocity. inasmuch as the speed of sound of air (1100 ft./sec. at room ternperature) is approximately equal to the magnitude of the blade speed that is permissible due to structural limitations imposed by stress, open cycle gas turbine applications have required that the type of blading utilized be such that the ratio of maximum gas speed to the maximum blade speed is minimized rather than maximized.

However, when dealing with such `gases as helium or hydrogen as the working liuids in an axial how compressor, the sonic velocities involved are in excess of 4500 ft./sec., and the requirements imposed on blade structures used for such applications are that the highest possible gas speeds be induced for a given blade speed to accomplish the maximum amount of compression work. Accordingly it can be seen that stress limitations, which are substantially the same when working with air or with such gases `as helium and hydrogen, necessitate the use of an axial flow compressor having a plurality of stages or alternately the utilization of a centrifugal compressor 4to accomplish a maximum amount of compression work.

Various of the ldifficulties encountered through the utilization of conventional multi-stage axial ow compressors stem from the fact that the amount of compression work that can be accomplished for a given blade speed (blade speed being limited by stress) depends directly on the amount of gas deflection that can be achieved by the chosen blade configuration. This deflection is, of course, limited by the extent that too rapid an expansion of the effective flow section accompanying the passage of the gas results in catastrophic expansion and similar losses. So long as a pressure rise issought through the principle of diffusion, the amount of deflection that can be effected in such a compressor is substantially limited to a small fraction of the angle at which the gas initially enters each stage.

It is known that lthe work `done per compressor stage is proportional to the product of the blade speed and the net change in whirl components of the gas velocity produced by the rotor. Therefore, the net work is directly dependent upon the difference in the tangents of the rotor entry and exit angles. However, because the blade deflection limitations previously described are so severe, the difference in the tangents is only a fraction of the magnitude of the initial tangent of the entry angle 3,112,3hh Patented Ecc. 3, 1963 and the net compression work is correspondingly small.

if a pressure rise is not desired as a direct result of the passage of gas through a blade row while at the same time a Substantial amount of gas deflection is sought, this deflection can be realized without the onset of the losses previously referred to. Such blade designs effectively produce a change in sign of the gas angle (measured relative to the axial direction) without decreasing the magnitude thereof. These blades in passing the gas from a positive (-1-) angle to a negative angle of the same magnitude pass the gas through a zero angle. This does not create a major problem inasmuch as the blade is progressively thickened to a maximum thickness at the middle thereof so that no local flow passage section increase corresponding to the local flow angle reduction results. Therefore, it can be seen that it is the change of the elective gas iiow passage section that causes the high losses previously referred to and not the change in the 'gas angle themselves.

lf an `arial iiow compressor is provided having rotor and Vstator blade profiles which are substantially symmetrical and suitably proportioned with individual sections to effect diffusion and deflection of the gas flow, various of lthe limitations which reduce the amount of effective compression wori; that can be accomplished by each stage ycan be obviated. More particularly, if each of the symmetrical rotor and stator blade rows is provided with a section for diffusing the gas flow passing therethrough with a corresponding static pressure increase and a second sect-ion for effecting `a substantial deflection of the gas flow without a corresponding pressure increase substantially more work per compressor stage can be achieved than can be obtained from a conventional compression stage operating at the same or even a somewhat higher blade speed.

It is a prime object of the present invention to provide a new and improved compressor blade structure which effects a large pressure rise at a relatively low bla-de speed.

A further object of the invention resides in the provision of an improved compressor blade structure which yields a high degree of compression while utilizing a relatively few number of stages.

Still another object of the invention is to provide a symmetrical blading configuration which can be adapted for use in an axial flow compressor unit; the rotor and stator stages or" which are each provided with a blade configuration to effect the diiusion of the `gas flow passing therethrough and a blade configuration to provide the separate function of deflecting the gas through a desired angle without a pressure increase so that a maximum amount of compression work at a selected blade velocity can be achieved.

A more finite object of the invention is to provide a blading configuration which is capable of compressing a fluid medium while operating at relatively low rotational velocity and which can be suitably adapted for utilization in any number of axial flow compressors and similar fluid working applications.

Other objects and advantages of the present invention will become apparent from the following detailed description of a preferred embodiment thereof, when considered in conjunction with the accompanying drawings wherein:

FIGURE l is a fragmentary sectional view of a preferred embodiment of the compressor blade structure as adapted for utilization in a conventional axial flow compressor unit;

FIGURE 2 is a fragmentary diagrammatic plan View of the rotor and stator components of one stage of a compressor as contemplated by the present invention;

FIGURE 3 is a-fragmentary sectional view taken along the line 3 3 in FIGURE l;

aliases FIGURE 4 is a fragmentary diagrammatic plan view corresponding to FIGURE 2 but illustrating another embodiment of the invention; and

FIGURE 5 is still another fragmentary diagrammatic plan view of a third embodiment of the compressor blade structure contemplated by the present invention.

A preferred embodiment of an improved compressor blade structure constructed in accordance with the provisions ot the present invention is best illustrated in FlG- URES 2 and 4. As depicted in the drawings, an axial flow compressor unit is adapted with a conventional rc action rotor blade row that is followed by an impulse or iiow reversing rotor blade row having an equal or greater number of blades. The reaction and impulse rotor blade rows, which are mounted for concomitant rotation in lixed relation on a driven shaft of the compressor unit, are followed by a pair of stator blade rows that are identical to the rotor blade rows although reversed by 180 (ie. a mirror image thereof). The reaction blades of both the rotor and stator blade rows function to effect the diffusion of the gas flow during the passage of the gas therethrough, and the impulse blades accomplish a substantial deection of the diffused gas ilow without a corresponding static pressure increase. This combination of reaction and impulse blade rows results in the production of a maximum amount of compression work per stage for a given blade velocity.

FEGURE 5 illustrates still another embodiment of the compressor blade structure contemplated by the present invention. As depicted in the drawing, this embodiment utilizes a rotor of pure impulse or ow reversing blades. On additional section of blades is utilized, which is an extension of the stator reaction blade section. In this alternate embodiment, a pressure rise through the principle of diffusion is effected in the reaction section of the stator blade row while the function of the impulse rotor stage and impulse section of the stator stage is to accomplish delection of the gas low during the passage thereof through these blade sections.

As illustrated in FlG'URES l and 3, a compressor, adapted with one preferred embodiment of the blade structure contemplated by the present invention, includes a housing lil having an inner wall that encompasses one or more compressor stages, each of which includes a dual rotor blade row 11 and a. dual stator blade row 12. Each dual rotor blade row il includes a row containing a plurality of reaction blades lia and a row having a corresponding number of impulse or low reversing rotor blades 11b. The blades lla and 11b extend radially outwardly from a hub i3 which is secured for rotary movement to a driven shaft 1 4.

The blade root of each of lthe rotor blades 11a and 1lb is structurally secured to a base plate or platform 16. Each of the base plates i6 is formed within a dove tail section 16a that is iixedly secured within a suitably proportioned slot i7 formed on the periphery of the hub 13. Accordingly, the cylindrical hub 13 is provided with a plurality of spaced-apart slots i7 about the periphery thereof wherein the rotor blades 11a and 1lb are secured for rotation therewith. The stator blades 12a and 12b extend radially inwardly from the wall of the housing l() between alternate dual rotor blade rows. More particularly, portions of the inner wall of the housing 1G have suitably proportioned slots it provided therein. Each of the slots i9 are adapted to accommodate a dove tail section 2i. extending from a base plate or blade platform 22 whereto the blade roots of stator blades 12a and 12b are lixedly secured. The tips of the rotor and stator blades are spaced a suiiicient distance from the housing l0 and hub 13, respectively, so as to insure clearance therebetween during operation of the compressor.

As illustrated, the reaction and impulse blades Lia and lll) are situated in a diverging passage defined by a section of the inner wall of the housing i9. The len-.4ling edges of the reaction blades lla and Za are inclined towards the direction of the approaching fluid, and effect a deflection of the same by an amount comparable with that produced by conventional blade rows. The present invention dillers from previous practice by the introduction in each stage of the additional blade rows lb and i212, forming additional impulse rotors and stators respectively. The .unction of the impulse blade rows is to reverse the circumferential component of fluid velocity at the exit from the moving and stationary blades rcspectively. This change in gas direction effected in the impulse blade sections is by definition of this term, not accompanied by appreciable pressure increase; therefore, these rows are capable of very large turning angles without the onset of substantial losses. Because the stator blade row l2 is substantially identical to the rotor blade row lll (i.e. a mirror image thereof) substantially equal pressure rises are effected in the rotor and stator sections of each stage of the compressor (i.e. reaction blading).

ln the previously described embodiment, the number of flow reversing lades 11b is shown to be equal to the number of reaction blades 11a; however, this need not be the case nor desired under all operating conditions. Accordingly, as illustrated in FlGURE 4, there are twice as many impulse blades 1lb and Z/J in the impulse sections as there are blades 11a and lla in the reaction sections.

Alternately, as illustrated in FIGURE 5, the rotor section might be designed to include a single row of pure impulse or ow reversing blades 11b. -In this embodiment of :the invention, the single impulse rotor blade row effects the deflection of the gas while simultaneously producing `a substantial increase in the kinetic energy thereof. The resulting static pressure rise during the subsequent passage of the gas `ilow through the reaction blades 12a of the stator blade row yields an even greater amount of stage work than with the previously described embodiments.

The operation and capabilities of the improved compressor blade structure will best be understood from the following operational description and an illustrative example of the improved results obtained through the utilization of the disclosed blading.

The operational description which is applicable to either of 'the three embodiments, varying in accordance with the dilerences in the particular blading configuration, will be presented in conjunction with fthe single stage illustrated in FIGURE 2. The gas ow enters the inlet guide valves or prewhirl valves (not shown) of the compressor with a given axial velocity. The prewhirl blades impart a rotational component to the gas flow in a direction opposite to the direction of rotor rotation which is from left to right in PlGURE 2. The gas exiting from the prewhirl blades enters the reaction stage of the rotor at an angle al, which is designated as a positive angle for purposes of illustration. The reaction rotor blades da deliect the gas ow through a rather small angle and the gas leaves the reaction section at an exit angle a2, which is also positive but somewhat smaller' in magnitude than the angle al.

The gas tlow exiting the reacting section of the rotor blades enters the impulse section. The impulse rotor blades lib elect the deflection of the gas tlow through an angle of zero degrees so that the angle a3 at which the gas exits from the impulse section is substantially equal in magnitude but opposite to a2 as measured from the axis of rotation. Upon entering the stator blade row, which includes the reaction blades 12a and `the impulse blades 12b, at an angle a4, the gas undergoes substantially the same deflections as occurred in the rotor blade row. Since in the illustrated embodiment symmetrical rotor and stator blade rows are utilized, the tangle a4 is numerically `equal to the `angle al but opposite in sign.

Accordingly, it can be seen that accompanying the rather small deflection, which is accomplished by the reaction blades lila and 12a, there is a static pressure rise resulting from diffusion. However, as the flow is deflected or turned through a substantial angle by the impulse blades 11b and v12b no pressure increase is realized. Under certain circumstances it may be preferable to achieve 'a small pressure drop in the impulse section with a corresponding small increase in gas velocity lwhich would improve the overall efciency of the blading configuration.

With previously constructed blade configurations the rotor entry and exit angles have both been positive angles (i.e. the angles corresponding to `angles a1 and a3 in 'FIGURE 2.). However, in the present invention the entry angle a1 of the gas to the dual rotor blade row is positive while :the exit angle a3 is negative. -Accordingly, the -amount of work done by each stage i-s proportional to the numeral sum of the tangents of the angles al and a3. Consequently, the work done by the dual rotor blade row 1:1 and, more particularly, by the reaction bl-ades 11a and flolw reversing blades Illlb is several times greater than that previously realized with conventional compressor blade strfuctures constructed so that no reversal in the gas exit and entry angles is effected.

The primary distinction between the manner in which the gas would be |worlced by the blading configuration illustrated in FIGUR-E 5 would be that the impulse rotor blades 1lb" would function exclusively to turn or reverse the 'flow of the gas. This would effect an increase in the velocity of the gas prior to th-e passage thereof into the reaction blades of the stator sect-ion wherein a substantial static pressure rise 'would be realized as a result of the diffusion of the gas through the effective flow section defined by adjacent reaction blades 12a.

The following example of the higher work capacity realized with the compressor blade structure contemplated by the present invention manifests the advantages of such blading. A conventional axial flow compressor utilizing 50% reaction blading and with the rotor blades functioning at a speed of approximately'900 feet per second requires `seven stages to effect a certain degree of compression of a gas such as helium. The gas emanating from -a compressor of .the conventional type has an exit angle yielding a positive exit swirl.

1n contradistinct-ion to the high rotor speed and substantial number of stages required in such a conventional compressor, ia unit incorporating a preferred embodiment of the blade structure previously described and having `similar dimensions compresses helium gas to the same degree while utilizing only four stages with the reaction and impulse rotor blades being driven at approximately 450 feet per second. The gas emanating from the compressor utilizing the dual rotor blade rovvs has a negative exit swirl which is somewhat greater than that in the conventional compressor. This exit swirl is readily overcome by incorporating an additional row of reaction rotor blades in the last stage of the compressor.

A specific embodiment of the compressor blade structure Awhich would be suitable for use in the example outlined above might preferably have a tip diameter of approximately 21/2 feet. ln addition, the pitch/ chord ratio might appropriately be chosen in the range of approximately .8 to 1.0, depending upon the turning angle desired and the stress considerations involved. The tip/hub radius ratio of such a blading configuration might be chosen at approximately 1.4, this figure again being dictated by the particular application in which the bladin g is utilized.

-From the foregoing it yis apparent that a new and improved type of compressor blade structure has been provided which can effect the emcient compression of a gaseous fluid such as helium While utilizing a minimum number of compressor stages having rotor blade rows operating iat relatively low speed. 'ln addition, a blade structure is provided that is capable of being adapted for use in any number of other fluid circulating systems. For example, the blading structure contemplated by the present invention could be advantageously utilized in the free running turbo-compressor, which is disclosed and claimed in applicants copending application Serial No. 88,534, which was iiled on February l0, 1961. The neduction in blade speed that is realized with the blade structure hereinbefore described while the fluid is worked at substantially the same axial velocity makes this blading structure particularly suitable for this latter application.

lt should be understood that the above described embodiment is simply illustrative of an application of the invention. Numerous other arrangements ofthe described structural features may be readily devised by those skilled in the art which would embody the principles of the in- Vention and fall within the spirit and scope thereof. Various features of the invention are set forth in the following claims.

What is claimed is:

1. ln an axial flow compressor, a driven shaft, a housing surrounding the shaft that defines a passage for fluid flow therethrough and a blade structure which comprises (A) a rotor blade section and a stator blade section situated adjacent said rotor blade section in the direction of fluid flow;

(B) said rotor blade section including (l) a first blade row containing a plurality of blades secured to and extending outwardly from said driven shaft in aligned circumferential spaced relation,

(a) each of said blades having a tapered trailing edge and being positioned so that adjacent ones of said blades define diverging passageways which accommodate expansion of the fluid flow being circulated therethrough without effecting a substantial deflection thereof, and

(2) a second blade row containing a plurality of symmetrical blades secured`to said driven shaft adjacent said first blade row in the direction of fluid ow,

(a) each of said symmetrical blades having an enlarged central section and tapered leading and trailing edge sections inclined in the direction of shaft rotation,

(b) said symmetrical blades being positioned on said driven shaft in fixed relation to the blades of said first blade row so that the tapered leading edge of each of said symmetrical blades of said second blade row is aligned with the tapered trailing edge of the adjacent blade of said first blade row whereby the fluid flow exiting said first blade row of said rotor blade section is deflected through a substantial angle by the symmetrical blades of said second blade row without a corresponding pressure increase;

(C) said stator blade section including (1) a first row of tapered blades and a second row of symmetrical blades that are secured to and extend inwardly from the inner wall of said housing adjacent said rotor blade row in the direction of liuid iiow,

(2) the blades of said first and second stator blade rows being constructed and positioned on the inner wall of said housing so as to form a mirror image of said rotor blade rows.

2. In an axial flow compressor, a driven shaft, a housing surrounding the shaft that defines a passage for fluid flow therethrough and a blade structure which comprises (A) a rotor blade section and a stator blade section situated adjacent said rotor blade section in the direction of fluid flow;

(B) said rotor blade section including (l) a first blade row containing a plurality of blades secured to and extending outwardly from said driven shaft in aligned circumferential spaced relation,

aliases (a) each of said blades having a tapered trailing edge and being positioned so that adjacent ones of said blades define diverging passageways which accommodate expansion of the fluid iiow being circulated therethrough without effecting a substantial deilection thereof, and

(2) a second blade row containing a plurality of symmetrical blades secured to said driven shaft adjacent said rst blade row in the direction of fluid ow,

(a) each of said symmetrical blades having an enlarged central section and tapered leading and trailing edge sections inclined in the direction of shaft rotation,

(b) Said symmetrical blades being positioned on said driven shaft in fixed relation to the lades of said first blade row so that the tapered leading edge of each of said symmetrical blades of said second blade row is aligned with the tapered trailing edge of the adjacent blade of said iirst blade row whereby the fluid liow exiting said iirst blade row of said rotor blade section is deflected through a substantial angle by the symmetrical blades of said second blade row without a corresponding pressure increase;

(c) said second blade row also including a plurality of symmetrical blades at least one of which is positioned between each pair of said symmetrical blades that are aligned with the blades of said first blade row;

(C) said stator blade section including (1) a first row of tapered blades and (2) a second row of symmetrical blades that are secured to and extend inwardly from the inner wall of said housing adjacent said rotor blade row in the direction of lluid tiow,

(3) the blades of said irst and second stator blade rows being constructed and positioned on the inner wall of said housing so as to form a mirror image of said rotor blade rows.

3. ln an axial ilow compressor, a driven shaft, a housing surrounding the shaft that denes a passage for fluid ilow therethrough and a blade structure which comprises (A) a rotor blade section and a stator blade section situated adjacent said rotor blade section in the direction of tiuid flow;

(B) said rotor blade section including (l) at least one blade row containing a plurality of symmetrical yblades secured to said driven shaft for rotation therewith,

(a) each of said symmetrical blades having an enlarged central section and tapered leading and trailing edges inclined in the direction of shaft rotation so that the fluid iiow passing therethrough is deflected through a substantial angle without a corresponding pressure increase;

(C) said stator blade section including (l) a lirst blade row containing a plurality of tapered blades that extend inwardly from the inner wall of said housing in aligned spaced relation so that adjacent ones of said tapered blades deline diverging passageways which accommodate expansion of the iuid liow being circulated O o therethrough after exiting said rotor blade scction and (2) a second blade row of symmetrical blades extending inwardly irom said housing,

(a) each of said symmetrical blades having an enlarged central section and tapered leading and trailing edge sections inclined in a direction opposite to that of shaft rotation and positioned adjacent said first blade row so that a pressure rise and a deflection of the fluid flow are sequentially effected during passage thereof through said stator blade section after exiting said rotor blade section.

4. in an axial tlow compressor, a driven shaft, a housing surrounding the shaft that defines a passage for iluid flow therethrough and a blade structure which comprises (A) a rotor blade section and a stator blade section situated adjacent said rotor blade section in the direction of iluid liow;

(B) said rotor blade section including (1) at least one blade row containing a plurality of symmetrical blades secured to said driven shaft for rotation therewith,

(a) each of said symmetrical blades having an enlarged central section and tapered leading and trailing edges inclined in the direction of shaft rotation so that the fluid flow passing therethrough is deflected through a substantial angle without a corresponding pressure increase;

(C) said stator blade section including (l) a first blade row containing a plurality of tapered blades that extend inwardly from the inner wall of said housing in aligned spaced relation so that adjacent ones of said tapered blades define diverging passageways which accommo date expansion of the tluid ilow being circulated therethrough after exiting said rotor blade section and (2) a second blade row of symmetrical blades ertending inwardly from said housing,

(a) said second blade row including at least twice the number of blades as are cmployed in said first blade row,

(b) each of said symmetrical blades having an enlarged central section and tapered leading and trailing edge sections inclined in a direction opposite to that of shaft rotation and positioned adjacent said first blade row so that a pressure rise and a deflection of the iiuid iow are sequentially effected during passage thereof through said stator blade section after exiting said rotor blade section.

References Cited in the tile of this patent UNITED STATES PATENTS UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3,112,1866 December 3, 1963 Peter Fortescue It is hereby certified that error appears in the above numbered patent requiring correction and that the seid Letters Patent should read as corrected below Column 2 line 19, for "angle" read angles column 3, line 32, for "On" read One column 5 line 16, for "numeral" read numerical Signed and sealed this 5th day of May 1964.

(SEAL) Attest: ERNEST W. SWIDER EDWARD JQ BRENNER Attesting Officer Commissioner of Patents 

1. IN AN AXIAL FLOW COMPRESSOR, A DRIVEN SHAFT, A HOUSING SURROUNDING THE SHAFT THAT DEFINES A PASSAGE FOR FLUID FLOW THERETHROUGH AND A BLADE STRUCTURE WHICH COMPRISES (A) A ROTOR BLADE SECTION AND A STATOR BLADE SECTION SITUATED ADJACENT SAID ROTOR BLADE SECTION IN THE DIRECTION OF FLUID FLOW; (B) SAID ROTOR BLADE SECTION INCLUDING (1) A FIRST BLADE ROW CONTAINING A PLURALITY OF BLADES SECURED TO AND EXTENDING OUTWARDLY FROM SAID DRIVEN SHAFT IN ALIGNED CIRCUMFERENTIAL SPACED RELATION, (A) EACH OF SAID BLADES HAVING A TAPERED TRAILING EDGE AND BEING POSITIONED SO THAT ADJACENT ONES OF SAID BLADES DEFINE DIVERGING PASSAGEWAYS WHICH ACCOMMODATE EXPANSION OF THE FLUID FLOW BEING CIRCULATED THERETHROUGH WITHOUT EFFECTING A SUBSTANTIAL DEFLECTION THEREOF, AND (2) A SECOND BLADE ROW CONTAINING A PLURALITY OF SYMMETRICAL BLADES SECURED TO SAID DRIVEN SHAFT ADJACENT SAID FIRST BLADE ROW IN THE DIRECTION OF FLUID FLOW, (A) EACH OF SAID SYMMETRICAL BLADES HAVING AN ENLARGED CENTRAL SECTION AND TAPERED LEADING AND TRAILING EDGE SECTIONS INCLINED IN THE DIRECTION OF SHAFT ROTATION, (B) SAID SYMMETRICAL BLADES BEING POSITIONED ON SAID DRIVEN SHAFT IN FIXED RELATION TO THE BLADES OF SAID FIRST BLADE ROW SO THAT THE TAPERED LEADING EDGE OF EACH OF SAID SYMMETRICAL BLADES OF SAID SECOND BLADE ROW IS ALIGNED WITH THE TAPERED TRAILING EDGE OF THE ADJACENT BLADE OF SAID FIRST BLADE ROW WHEREBY THE FLUID FLOW EXITING SAID FIRST BLADE ROW OF SAID ROTOR BLADE SECTION IS DEFLECTED THROUGH A SUBSTANTIAL ANGLE BY THE SYMMETRICAL BLADES OF SAID SECOND BLADE ROW WITHOUT A CORRESPONDING PRESSURE INCREASE; (C) SAID STATOR BLADE SECTION INCLUDING (1) A FIRST ROW OF TAPERED BLADES AND A SECOND ROW OF SYMMETRICAL BLADES THAT ARE SECURED TO AND EXTEND INWARDLY FROM THE INNER WALL OF SAID HOUSING ADJACENT SAID ROTOR BLADE ROW IN THE DIRECTION OF FLUID FLOW, (2) THE BLADES OF SAID FIRST AND SECOND STATOR BLADE ROWS BEING CONSTRUCTED AND POSITIONED ON THE INNER WALL OF SAID HOUSING SO AS TO FORM A MIRROR IMAGE OF SAID ROTOR BLADE ROWS. 